Drying fiber string material



Patented Apr. 21, 1942 I DRYING FIBER STRING MATERIAL Peter D.Pl-ambeck, Chicago, 11]., assignor to Armour and Company, Chicago, 111.,a corporation 01' Illinois No Drawing. Application July -19, 1939,Serial No. 285,457

2 Claims.

4 homogeneous and strong by immersing the strand in suitable swellingagents, such as alkaline solutions. After such strings have been swollenthey are then deplumped and-finally dried. The drying problem has been adifiicult one to solve. The

wet strings cannot simply be placed in a drying atmosphere. Such strandsare of indefinite lengths and in prior practices they-have beensupported on pulleys in a'drying room where moisture is removed from thestring.

Drying rooms are frequently very long,- as much as 100'feet, and the wetstrands are led in parallel rows over a series of pulleys spaced as muchas 50 feet apart. Consequently, several hundred feet of strand materialwill be undergoing drying at any particular time. One of the desiredobjects in any drying process is to so-dry the strand that no breaksoccur in it during the drying stage. Thus, for example, the wet cord istaken directly from treating baths, usually a plain water-wash whichfollows the deplumping bath, and threaded over pulleys in the dryingroom as a continuous strand of indefinite length. The drying operationis continuous in the sense that the strand moves continu-. ously throughthe drying atmosphere. over the pulleys, and the dried strand iscollected in coils, or on spools.

In consequence, a drying room will contain several hundred feet ofstrand material undergoing drying, and under varying degrees of tension.During the drying operation as hitherto practised, any particulardesired tension cannot be maintained throughout the entire drying stage.without danger of breakage.

As practised hitherto, the dried strings sufier a loss of tensilestrength. This is probably because theouter layer of fibers in thestrand dries first, forming a relatively thin, dry outer shell while thecore within the string is still-wet. This outer shell tends to fractureand crack as the long strand is guided around pulleys in the dryingroom. The net result is that the actual cross section of the homogeneousportion of the strin is reduced with resultant reduction in tensilestrength. While this explanation may not be correct,-nevertheless, it isan observed fact that strings of this nature. when dried under the usualconditions of temperature and pressure, do frequently break while undertension.

I have, therefore, investigated the drying process, and I havediscovered that by observing certain specific values of j temperatureand humidity in the drying atmosphere I can obtain a string which isstrong and which will not break under the usual drying andfinishingconditions. By finishing conditions I mean those operations usuallyemployed after the string has been dried. Such operations are, forexample, sanding and polishing. By maintaining certain temperature andhumidity relationships which I- have discovered the outer layer in thestrand does not g dry too rapidly, and hence any cracking is avoided. Bythe process of the present invention the drying takes place moreuniformly and the outer layer does not completely dry until the innercore of the strand is substantially dry.

As stated, the present invention is directed primarily to the drying ofspun and twisted collagenous-fibrous materials which, in strand form,-

have been subjected to swelling and deplumping agents. I shall,therefore, describe my invention more particularly with reference tosuch cords.

These cords, which are similar to cat gut' in appearance, and which areused as sutures, tennis strings, musical instrument strings, and thelike,'are made from animal tendons or sinews. The dried animal tendon isfirst hammered to break the outer shell and release the fiber within theshell. These fibers are then carded, formed into a roving, the rovingspun into a yarn, and

a plurality of yarn strings twisted to form the final cord or strand.This strand is then immersed in swelling agents, usually dilutesolutions of alkalies, such as caustic soda. Such swelling agents causethe fibers in the strand to swell and the entire preassembled cord isthus rendered homogeneous. Before such a swollen strand can be used itmust be deplumped in a bath which neutralizes the alkali in the cord andcauses the strand to shrink back to normal size. Finally, the deplumpedcord is washed in water to remove chemicals used in the swelling anddeplumping. The washed cord can then either be directly subjected to thedrying conditions f the present process, or it can be first immersed inany suitable binding solution, such as serum albumin or egg albumin, andthen subjected to the drying operation.

The present invention is primarily directed to the drying operation andnot to the particular been made. is then run Over pulleys in a dryingroom in the usual way. I depart, however, at this stage from theteachings of the prior art, which have advocated a rather rapid drying.In my drying operation I maintain the atmosphere in the drying room atrelatively high humidity.

This distinguishes my process from the customary drying procedure whichhas hitherto employed atmospheric conditions of low humidity. In myprocess the drying temperature should range from about 75 F. to 90 F.and the relative humidity should range from about 83% to 89%. Moreprecisely the temperature in the drying room can be 76 F. with a wetbulb reading of 73 F. corresponding to a relative humidity of 84%. Underthese condition drying is substantially complete in about three-quartersof an hour, depending largely on the diameter of the cord. The strings,as they come oil the drying .line will ordinarily contain about to ofmoisture, some of which will be lost during subsequent handling. Thestrings are' not dried to bone dryness. But they are: dried under suchconditions that much less tendency to fracture and break is realized,and the strings retain their original tensile strength.

In another example, the strings, as prepared above, are dried in adrying atmosphere having a temperature of about 90 F. and a relativehumidity of 89%.

After drying the strings so prepared can be finished by sanding andpolishing, and can be dyed to give the brightly colored tennis stringsof commerce. Or they can be polished and finished to give strings forviolins, harps, and other washed; and after the tanning treatment thestrings are then dried in the manner described above.

The drying processes of the present invention are particularlyapplicable to the drying of strings made in accordance with my'co-pending application, -Serial No. 285,458 filed July 19, 1939,

chemical treatments applied to the preassembled iwherein I describe theswelling of the Pr'eassembled sinew fibers in a plurality of alkalinebaths of increasing concentrations whereby the fiber angle in the stringis maintained throughout the process.

I Although, in the above description, I have re-' ferred to specifictemperatures for the drying air, I regard humidity as more importantthan the temperature of the air. By maintaining the humidity relativelyhigh I'can operate the drying temperaturesconsiderably above thosehitherto used without destroying desirable characteristics in thefinished string. The temperature and humidity relationships should besuch that no apparent swelling of the string, as may be judged bygauging, occurs-during the drying process. That is to say, the diameterof the string should progressively decrease during the drying ratherthan increase. The present invention deliberately avoids the use of hot,dry air as the drying medium. Such drying conditions are detrimental.But because of the relatively high humidity employed in the present casedrying temperatures can exceed those hitherto used.

Although I have more specifically referred to the preparation of thestrands prior to drying by chemical treatment involving the use ofalkalis, my invention is applicable to strands or strings which havebeen processed in acid' solutions in accordance with prior art practice.

Having thus described my invention, what I claim is:

1. In the drying of homogeneous strings, while in the form of long,continuously moving lengths,

and which have been prepared from collagenous fibers which have beenspun and the string thus formed swollen with alkaline swelling agentsand thereafter deplumped and washed, the step which comprises exposingthe wet strings, as long, continuously moving lengths, to an atmospherehaving a temperature of about 75F. to 90 F. and

' which has a relative humidity from about 83% 2. In the drying ofhomogenous strings, while in the form of long, continually-movinglengths,

- and which have been prepared from collagenous has a relative humidityfrom about 83% to 89%.

PETER D. PLAIVLBECK.

